What version of Android are you on? Android 12 or below? It was removed entirely in Android 13. It can be “patched back in” on a custom ROM, but doing so breaks the recents screen due to incompatible changes made to the system launcher (which handles the recents screen for… some reason).
Or maybe you have a Samsung or other phone that has their own 2 button implementation. But as far as I’m aware, it’s gone from AOSP as of Android 13 :(